(1) Field of the Invention
This invention relates to a coating method and a coating apparatus for applying a coating solution, e.g. photoresist, uniformly over surfaces of substrates such as semiconductor wafers, glass substrates for liquid crystal display panels, or mask substrates for semiconductor manufacturing apparatus. More particularly, the invention relates to a technique for applying a coating solution in an inkjet mode to substrates.
(2) Description of the Related Art
Conventionally, a spin coat method is known as the coating method for applying a coating solution uniformly over each substrate. The spin coat method is a technique for forming a thin film of the coating solution on a substrate surface by supplying the coating solution to a central position on the surface of the substrate, and rotating the substrate at high speed to spread the coating solution over the substrate by centrifugal force. In the spin coat method, an excess part of the coating solution is spun off the edges of the substrate to be wasted in the course of the high speed rotation of the substrate. This constitutes a bad use efficiency of the coating solution.
On the other hand, techniques for forming a thin film of a coating solution on a substrate surface have been proposed in recent years, which supply the coating solution to the substrate surface using nozzles in an inkjet mode (as disclosed in Japanese Unexamined Patent Publication H8-250389 (pages 4-5 and FIG. 1) and Japanese Unexamined Patent Publication No. 2002-66391 (pages 3-6 and FIGS. 1-7), for example). In the inkjet mode, a thin film of a coating solution is formed on a substrate surface by supplying the coating solution in a required minimum quantity while moving the substrate and the nozzles relative to each other. Therefore, the inkjet mode can improve the use efficiency of the coating solution over the spin coat method.
However, according to the inkjet mode, fine particles of the coating solution are jetted off to the surface of a substrate, which tends to leave irregularities of the particles on the thin film of the coating solution formed on the substrate surface. As a result, the inkjet mode has a problem of lacking in uniform film thickness.